Field of the Invention
The present disclosure relates to the field of sensor, specifically to a sensor system using a piezoelectric microcantilever coupled with a resonating circuit.
Description of Related Art
Development of nano- and micro-electromechanical systems (NEMS and MEMS) has been made possible due to advances in nanotechnology. Reducing the dimensions of electromechanical systems to micro- and nano-scale has enabled the identification of biological molecules utilizing mechanical biosensors. High-throughput diagnosis and analytical sensing require advanced biosensing tools exploiting high affinity of biomolecules. There are a number of useful biosensing techniques such as electrophoretic separation where spatiotemporal separation of analytes is possible. Another important technique is identifying the changes in the mass or optical properties of target proteins using spectrometric assays. Identification and quantification of target biomolecules due to high affinity which is based on molecular recognition has been known as one of the most reliable biosensing mechanisms.
There are two main elements in a biosensor which are i) sensitive biological receptor probe which interacts with target proteins and ii) transducer which transforms the molecular recognition into a detectable physical quantity. There are a number of instruments equipped with these elements developed for bio-detection such as quartz crystal microbalance (QCM), surface plasmon resonance (SPR), enhanced-Raman spectroscopy, field effect transistors (FET) and MicroCantilever (MC)-based biosensors. Among these techniques, MC-based biosensors have emerged as an outstanding sensing tool for being highly sensitive, label-free, and cost effective. All MC-based sensors are equipped with a read-out device which is capable of measuring the mechanical response of the system. There are a number of conventional read-out systems among which optical based measurement is the most commonly used. They have been widely used in atomic force microscopy (AFM) and measure the mechanical changes of the system by calculating the difference of the angle of laser beam reflected from the surface of the cantilever. Even though being sensitive, there are certain limitations with this technique which are mainly high cost, being bulky and surface preparation requirement. Moreover, laser alignment and adjustment and the requirement of the sample solution and liquid chamber to be transparent impose serious challenges for adopting such a method as a read-out device in molecular sensing tools.
There are two main operational modes of MC-based sensors which are i) static and ii) dynamic modes. Most of the studies regarding identification of molecular affinities have been performed in the static mode where the induced surface stress as a result of deflection of MC from a stable baseline to measure molecular binding. On the other hand, in dynamic mode, the system is brought into excitation at or near its resonance frequency. The shift in the resonance frequency as a result of molecular recognition yields a good insight into the amount of adsorbed mass.
One important factor determining the success of all biological sensors performing based on analytical sensing of high affinity of biomolecules is the ability of the sensor to operate in liquid media with high sensitivity. However, high dampening and viscous effects of solutions indeed impose a burden on the performance of biological sensor in a liquid environment. Some approaches have been developed to overcome this challenge by i) operating the system in humid gas-phase media, and ii) dipping the sensing probe in the solution, and then removing and desiccating it and finally doing the measurement. However these methods increase the interference of unspecific biomolecules, and prohibit real-time and continuous monitoring.